1. Field of the Invention
The present invention relates to a heat pipe for a heat sink assembly, and particularly to a heat pipe which has an outer pipe incorporating an inner pipe therein.
2. Related Art
Historically, the use of metallic heat sinks has been sufficient to provide the thermal management required for most electronic cooling applications. However, with a new breed of compact electronic devices requiring dissipation of larger heat loads, the efficacy of metallic heat sinks is sometimes limited due to the weight and physical size of the heat sink required to perform the cooling. Accordingly, the use of heat pipes is becoming an increasingly popular solution of choice.
Conventional heat pipes are sealed vacuum vessels that are partly filled with working fluid. When external heat is input at an evaporating end, the working fluid is vaporized, creating a pressure gradient in the heat pipe. This pressure gradient forces the vapor to flow along the heat pipe to a cooler section (a condensing end) where it condenses and releases latent heat that was absorbed in the process of the vaporization. The condensed working fluid then returns to the evaporating end through a wicking structure that provides capillary forces. There are several types of wicking structures in common use, including grooves, screening, fibers, and sintered metal powder. An example of a conventional wicking structure is disclosed in Taiwan Patent Application No. 86206429. A plurality of fibers is formed at an inner face of the heat pipe. At least one V-shaped groove is defined in each fiber along an axial direction of the fiber. Another example of a conventional wicking structure is disclosed in Taiwan Patent Application No. 88209813. A piece of metal screening is attached to an inner face of a heat pipe. The metal screening has a plurality of through holes, and a plurality of grooves defined in a surface thereof along an axial direction of the heat pipe. However, the capillary forces provided by these conventional wicking structures are often still not sufficient. Furthermore, the vapor and the condensed fluid flow in the same pipe in opposite directions and interfere with each other. This retards the heat dissipating efficiency of the heat pipe.
Thus a heat pipe that can overcome the above-described problems is desired.